When particles of powdered material are transferred through a pipeline by means of compressed air flow, their travel direction can be changed by mounting an elbow A in the pipeline as shown in FIG. 1. Particles moving from a straight pipe into the elbow A will immediately impact upon a turning portion of elbow A and bound therefrom to change their travel direction. Such constant and immediate impact of the particles upon the wall of the elbow causes the elbow to wear out quickly and even break. Moreover, fierce turbulence in the air flow is caused by these bounded particles in the elbow to reduce the flow speed of particles and may dangerously clog the pipeline. To solve such problems, it is usually effective to increase the air pressure inside the pipeline and to introduce secondary compressed air into the elbow from a front end thereof, so as to speed up the flow of the particles. However, these actions only speed up the wearing down of the elbow.
To overcome the wearing problem existing in ordinary elbows, an elbow B, having a larger radius of curvature, as shown in FIG. 2, is developed. It is expected that the larger radius of curvature of the elbow B will expand an area on which the particles impact and thereby, the unit pressure thereof is reduced. However, in a practical application of the elbow B, it indicates that a longer travel distance provided by the elbow B will only lengthen the area where a turbulence would occur. In the case where a low melting point material is transported, filaments adversely occur due to heat generated by a material with an excess amount of friction with the wall of the elbow B.
Another solution adopted is to use a tee C. As shown in FIG. 3, one of the three ends of the tee C is sealed so that a fight angular path is formed in the tee C. Particles or powdered material are deposited and accumulated at the sealed end of the tee C function to some extent to avoid the wearing down of the tee at that portion. However, a portion of the wall of the tee C, near an outlet thereof, angularly opposite to the sealed fight angular portion, is inevitably worn out due to constant abrasion by those particles rebounded from the sealed right angular portion. And, a clogged pipeline may still be the result.
To enhance the wearability of the elbow or tee for such purpose, there are ceramic-lined elbows in the market with the expectation that the hardness of the ceramic material may overcome the problem of rapid wearing of the elbow. However, such ceramic-lined elbows require an extremely high manufacturing cost while it prolongs only limited times of usable life of the elbow compared to conventional elbows. That is, the ceramic elbow is not economical when viewing from this standpoint. Moreover, particles of broken ceramic materials mixed with transferred materials can cause a considerably big problem to the quality of the transferred materials.